It is very important to maintain vehicle pneumatic tires at the proper pressure. Underinflated tires can be unsafe and result in waste of fuel. Although manufacturers of automobiles and tires recommend maintenance of specified air pressures, with frequent checking, such recommendations are seldom followed since, for the average motorist, checking tire pressure is a relatively dirty and inconvenient process.
When checking tire pressure a motorist typically must unscrew a tire valve cap, press a conventional air pressure gauge having an indicator against the tire valve end, remove the gauge, read the pressure indicated thereby, and then reattach the cap. This procedure must of course be carried out for all four tires of an automobile (more in the case of certain trucks and specialty vehicles). Motorist aggravation and frustration can be compounded by misadventure such as cap loss or damage.
It is known that some motorists employ miniature pressure gauges permanently installed on tire valve stems which will visually indicate loss of air pressure. Such arrangements are relatively expensive, affect wheel balance, and are not in widespread use.
Some military vehicles and a few trucks and specialty civilian vehicles employ complex and costly systems which enable a driver to monitor tire pressure from inside the vehicle, in some cases even when the vehicle is moving. Ordinary passenger cars do not offer such devices due to their relative complexity and high expense. Reliability is also a problem in connection with such systems.
The following patents are believed to be representative of the current state of the prior art in this field: U.S. Pat. No. 3,580,064, issued May 25, 1971, U.S. Pat. No. 2,508,849, issued May 23, 1950, U.S. Pat. No. 2,717,450, issued Sep. 13, 1955, U.S. Pat. No. 2,435,644, issued Feb. 10, 1948, U.S. Pat. No. 1,404,425, issued Jan. 24, 1922, U.S. Pat. No. 2,997,976, issued Aug. 29, 1961, U.S. Pat. No. 2,712,808, issued Jul. 12, 1955, U.S. Pat. No. 1,363,825, issued Dec. 28, 1920, U.S. Pat. No. Des. 59,364, issued Oct. 11, 1921, and Italian Patent No. 290,929, issued Dec. 3, 1931.
U.S. Pat. No. 2,435,644 (Beckett et al) is worthy of particular comment in that it shows a device for comparing the wheel height of a vehicle under load for the purpose of adjusting the internal air pressure of each tire to compensate for the actual load borne by each tire. Deflected and undeflected portions of each tire are measured and a tire's air pressure is to be increased when it is under a heavy load and decreased when the load on that tire is less. The Beckett et al device employs an elongated cross bar which is not movable to a retracted position and which must be relatively long since the Beckett et al system requires measurement of the distance between the top of the tire and the top of the wheel rim. Conversion scales are employed on the device which must be utilized to fulfill the objectives of the Beckett et al invention.
The Beckett et al device can retain only one measurement, and since the Beckett et al method requires eight measurements for a four-wheel vehicle, in connection with each trip the user must separately record each measurement, compare them to specified guidelines, adjust air pressures, and then remeasure until each tire conforms to the guidelines. Such an approach is highly inconvenient and time consuming as compared to the apparatus and method of the present invention wherein the operator can monitor each pair of front and rear tires quickly and efficiently. As mentioned above, the elongated arm of Beckett et al cannot be moved between an extended position and a retracted position to facilitate storage of the apparatus. Thus, the extended arm is always in a condition which will render it susceptible to maladjustment or even damage.
The Italian Patent No. 290,929 to Pietro et al noted above is not suitable for measuring tire pressure, such device being utilized for the measurement of people or animals. The movable height measuring element of Pietro et al is continually spring biased and no provision is made in Pietro et al for locking the height measuring element or indicator in position relative to the rest of the device.